The majority of fluorescent lamps require the use of an inductor known as a ballast. The ballast is connected in series with the lamp to prevent excess current from flowing through an ionized plasma of a lighted lamp. If the ballast did not limit the current flow through the lamp, the excessive current would prematurely consume the filaments or cathodes and the interior phosphorescent coating which converts photon energy from the ionized plasma into illumination, thereby decreasing the useable lifetime of the lamp.
Although the ballast is effective to reduce the lamp current to levels which result in reasonable lamp lifetimes, the effect of the series-connected ballast is to reduce the voltage available to energize the plasma. The general rule is that the operative working voltage of the plasma must be no greater than one half of the voltage available from the mains power supply driving the lamp (such as 110, 120 or 220 volts) for a simple reactor ballast to work satisfactorily.
In general, high illumination-efficiency fluorescent lamps require higher voltages to achieve the higher levels of illumination. These higher illumination-efficiency lamps generally require separate, costly and sizable power supplies to boost the power supply mains voltage to a usable level. Such separate power supplies frequently employ autotransformers to obtain the increased voltage. The separate power supplies also contribute to the cost of the high illumination efficiency fluorescent lamps.
In an attempt to increase the voltage to a level satisfactory for use with a high illumination-efficiency fluorescent lamps, resonant energy storage, voltage-boosting circuits have been used in conjunction with the ballast. The resonant voltage boosting circuits store energy from the power mains and release the stored energy to the lamp as an oscillating, resonant driving voltage which is greater than the voltage of the power mains. The resulting higher voltage makes it possible to ignite and operate the higher illumination efficiency fluorescent lamps.
While a resonant circuit is effective in raising the voltage applied to the lamp, the characteristics of the resonant circuit either prohibit or limit the ability of a conventional fluorescent lamp starter circuit, such as a "glow bottle," to start or ignite illumination from the lamp. Generally, a very high voltage spike or pulse is required to initially establish an ionized conductive plasma in the lamp, after which the ignited plasma is sustained by the normal operating voltages. The resonant energy storage circuit appears to diminish the effect of the high starting voltage pulse or may even prevent the generation of the high voltage starting pulse altogether. Separate starter circuits are therefore required, which add cost and complexity. Without the capability of reliably starting or igniting the fluorescent lamp, the practical benefits gained from the resonant energy storage voltage boosting circuit are diminished or completely eliminated.
It is with respect to these and other considerations that the improvements from the present invention have resulted.